Metabolic flux in glucose/citrate co-fermentation by lactic acid bacteria as measured by isotopic ratio analysis

Goupry, StÃ©phane; Croguennec, Thomas; Gentil, Emmanuel; Robins, Richard J.

doi:10.1111/j.1574-6968.2000.tb08896.x

Cited by 21 publications

(20 citation statements)

References 14 publications

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“…This metabolic process leads to the formation of a number of minor products important for the organoleptic properties of cheese (19). The present report clearly shows that although E. faecalis FAIR-E 229 cannot catabolize citrate in the presence of glucose, it has the ability to metabolize citrate in milk in the presence of lactose.…”

Section: Discussionmentioning

confidence: 62%

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Citrate Metabolism by Enterococcus faecalis FAIR-E 229

Sarantinopoulos

Kalantzopoulos

Tsakalidou

2001

Appl Environ Microbiol

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Citrate metabolism by Enterococcus faecalis FAIR-E 229 was studied in various growth media containing citrate either in the presence of glucose or lactose or as the sole carbon source. In skim milk (130 mM lactose, 8 mM citrate), cometabolism of citrate and lactose was observed from the first stages of the growth phase. Lactose was stoichiometrically converted into lactate, while citrate was converted into acetate, formate, and ethanol. When de Man-Rogosa-Sharpe (MRS) broth containing lactose (28 mM) instead of glucose was used, E. faecalis FAIR-E 229 catabolized only the carbohydrate. Lactate was the major end product, and small amounts of ethanol were also detected. Increasing concentrations of citrate (10, 40, 70, and 100 mM) added to MRS broth enhanced both the maximum growth rate of E. faecalis FAIR-E 229 and glucose catabolism, although citrate itself was not catabolized. Glucose was converted stoichiometrically into lactate, while small amounts of ethanol were produced as well. Finally, when increasing initial concentrations of citrate (10, 40, 70, and 100 mM) were used as the sole carbon sources in MRS broth without glucose, the main end products were acetate and formate. Small amounts of lactate, ethanol, and acetoin were also detected. This work strongly supports the suggestion that enterococcal strains have the metabolic potential to metabolize citrate and therefore to actively contribute to the flavor development of fermented dairy products.The industrial importance of lactic acid bacteria is mainly based on the ability of these organisms to rapidly ferment carbohydrates and to convert them into lactic acid and, to a lesser degree, into other flavor compounds. Lactic acid provides protection against spoilage by nonacidophilic organisms. On the other hand, many lactic acid bacteria are also able to ferment a number of noncarbohydrates, including citrate. Citrate metabolism plays an important role in many food fermentations involving lactic acid bacteria, since it occurs in many natural substrates, such as milk, vegetables, and fruits (21). The behavior of lactic acid bacteria may differ from one species to another, and not all lactic acid bacteria are able to metabolize citrate (24).The ability to metabolize citrate is invariably linked to endogenous plasmids that contain the gene encoding the transporter which is responsible for citrate uptake from the medium (2). Since citrate is a highly oxidized substrate, no reducing equivalents, such as NADH, are produced during its degradation, which results in the formation of metabolic end products other than lactic acid. Some of these end products, such as diacetyl, acetaldehyde, and acetoin, have very distinct aroma properties and significantly influence the quality of fermented foods (20). For instance, diacetyl determines the aromatic properties of fresh cheese, fermented milk, cream, and butter (12) but is considered the most important off-flavor compound in the brewing process and in the wine industry (22). The breakdown of citrate also results in the p...

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Section: Discussionmentioning

confidence: 62%

“…This conclusion was based on the inability of the lactic acid bacteria to grow in batch cultures to which excess citrate was added as the sole energy source (6,7). Sometimes, lactic acid bacteria need sug- ars, such as glucose or lactose, as cosubstrates in order to consume citrate (7,17,19).…”

Section: Discussionmentioning

confidence: 99%

Citrate Metabolism by Enterococcus faecalis FAIR-E 229

Sarantinopoulos

Kalantzopoulos

Tsakalidou

2001

Appl Environ Microbiol

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“…Most of them need a sugar as a co-substrate (Cogan 1987;García-Quintáns et al 1998;Goupry et al 2000). At the beginning of ripening, a low amount of glucose derived from lactose catabolism can be found in cheeses.…”

Section: Discussionmentioning

confidence: 97%

Citrate metabolism by Enterococcus faecium and Enterococcus durans isolated from goat’s and ewe’s milk: influence of glucose and lactose

et al. 2007

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Citrate metabolism by Enterococcus faecium ET C9 and Enterococcus durans Ov 421 was studied as sole energy source and in presence of glucose or lactose. Both strains utilized citrate as the sole energy source. Enterococcus faecium ET C9 showed diauxic growth in the presence of a limiting concentration of glucose. Neither strain used citrate until glucose was fully metabolized. The strains showed co-metabolism of citrate and lactose. Lactate, acetate, formate, and flavour compounds (diacetyl, acetoin, and 2,3-butanediol) were detected in both strains. The highest production of flavour compounds was detected during growth of E. durans Ov 421 in media supplemented with citrate-glucose and citrate-lactose. Citrate lyase was inducible in both strains. Acetate kinase activities presented the highest values in LAPTc medium, with E. faecium ET C9 displaying a specific activity 2.4-fold higher than E. durans. The highest levels of alpha-acetolactate synthase specific activity were detected in E. durans grown in LAPTc+g, in accordance with the maximum production of flavour compounds detected in this medium. Diacetyl and acetoinreductases displayed lower specific activity values in the presence of citrate. Enterococcus faecium and E. durans displayed citrate lyase, acetate kinase, alpha-acetolactate synthase, and diacetyl and acetoin reductase activities. These enzymes are necessary for conversion of citrate to flavour compounds that are important in fermented dairy products.

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“…Gá lvez, Loiseau, Paredes, Barel, and Guiraud (2007) have shown that citric acid was almost completely degraded before glucose and fructose uptake started during cacao fermentation. Using pure cultures of lactic acid bacteria mainly strains of Lactococcus lactis, Goupry, Croguennec, Gentil, and Robins (2000) have also described a similar phenomenon with citric acid being used first before the sugars.…”

Section: Resultsmentioning

confidence: 96%